Adding data to new record with URL formula but having problems with order of operations

Len, can you post your code separately, as its not possible to read in a screen shot, nor copy paste to suggest fixes.

This is the formual to generate the next PO number:

var text jobNumber = ToText([Job Number]);
var number numberOfFollowingZeros = 4-Length(ToText([# of POs]+[Missing Sequence]+1));
var text followingZeros =
    Case
    (
    $numberOfFollowingZeros
    ,3,"000"
    ,2,"00"
    ,1,"0"
    ,0,""
    );
var text finalNumber = ToText([# of POs]+1+[Missing Sequence]);
$jobNumber & $followingZeros & $finalNumber



This is the Add button URL formula:

URLRoot() & "db/" & [_DBID_PURCHASE_ORDERS] & "?a=API_GenAddRecordForm&_fid_13=" & URLEncode ([Record ID#2])& "&_fid_21=" & URLEncode ([Next Purchase Order Number])  &"&z=" & Rurl()

I just fixed the issue where 9, 99 and 999 add an extra zero by adding a +1 to the character count. The issue with zero POs is still persisting. 

I assume that you have a Summary field to count the number of children.  Is the field property on that field set to treat blank as zero?

In all of my panic, frustration, anxiety and 50 tabs open failed to review that simple "treat blank as zero" checkbox on the field properties. I am very grateful that you were able to point his out as it solved my issue immediately.

Te other option is to wrap a field that might be null with

Nz([my field])

The Nz() function will turn a null into a zero, else just the value it is, if not null.

But I really try to avoid that as it clutters up the code.